The present invention relates to an improved power supply circuit for an actuator which is controlled by a travel control device for an automobile.
In order to ensure safe travel of a vehicle, an antilock control device (ABS) and a vehicle stability control device (ASC) are used. For example, in an ABS control device, actuators such as solenoid valves in a brake hydraulic circuit and an electric motor for a hydraulic pump are opened and closed or turned on and off in response to commands from an electronic control circuit for brake control of vehicle wheels.
As shown in FIG. 3, heretofore, the line for supplying power to a plurality of loads L1 and the line for supplying power to the load L2 are provided as independent lines in which signals generated by switches (SW1, SW2) 11a, 11b through voltage increasing circuits 10 in power lines from a battery power source are fed to driving circuits 14a, 14b through control lines 12a, 12b. 
The electric motor 15b is activated when the pressure of the brake circuit is increased by a hydraulic pump in a hydraulic circuit during antilock control. On the other hand, the circuit 14a for supplying power to the solenoid valves 15a is always in a standby state when the electric motor 15b is ON. Thus, if a power is supplied through a line common to both, there is a possibility that upon the activation of the line for the electric motor 15b, one solenoid valve or two may malfunction. In order to avoid this, the two lines are provided independently of each other.
As described above, in order to prevent any influence of activation and deactivation of the motor on the circuit for supplying an electric power to the solenoid valves 15a, providing the power lines independently of each other is most effective. But for this purpose, it is necessary to provide a voltage increasing circuit for each line. This is disadvantageous in view of higher cost.
Thus, it is conceivable to provide a power supply circuit in which a single voltage increasing circuit is provided and the line for supplying power is split into two lines, one to supply power to electromagnetic valves and the other to supply power to an electric motor. Such a power supply circuit is shown in FIG. 4A. As shown, voltage VB fed from a battery power source is increased in a voltage increasing circuit 10. This voltage supply line is split into two. Signals by SW1 in one line are input into a driving circuit 14a (FET transistor) for loads L1 to supply power to the loads L1, whereas signals of SW2 in the other line are input into a driving circuit 14b (FET transistor) for a load L2 to supply power to the load L2.
The operation of the thus formed power supply circuit is shown in FIG. 4B. When the switch SW1 is turned on, a signal VG1 at the input point is input in the driving circuit 14a, and VG1 will be VB+increased V, which is supplied to the loads L1. After a predetermined time, when the switch SW2 is turned on, a signal VG2 at the input point is input in the driving circuit 14b, and VG2 will be VB+increased V, which is supplied to the load L2. But the moment that the switch SW2 is turned on, the voltage of the loads L, is taken to increase the voltage VG2 to the load L2, so that the voltage VG1 drops sharply, as illustrated in FIG. 4B. This state is similar to a state in which it is momentarily shut off. But later, VG1 and VG2 will increase at substantially the same rate. This is as if SW1 malfunctions, meaning that the activation of the loads L1 is influenced by the activation of the load L2.
An object of this invention is to provide a power supply circuit in which various actuators are controlled. In addition, measures are taken for one actuator that tends to be influenced by the behavior of another actuator, in which power is supplied to a plurality of control lines through a single voltage increasing circuit, which can be manufactured at an economical cost.